Blu LIFE 8, Service Manual, Page: 16 / 29

3.3 RX Circuit troubleshooting
3.3.1 RX circuit analysis
At first, The aerial signal of mobile phone received from antenna to RF connector, which is
a special part developed for RF test. By connecting RF cable to analyze spectrum, you can
measure the RF signal here. Signal from RF connector will be into the ASM which part in
PA IC.
Signal from PA go through the SAW(bandpass) filter, by unbalance transformation,
becoming two paths mutually discrepancy 180 degrees divide signal, and via the Matching
Circuit to the transceiver MT6166.
The Transceiver is the main IC of the radio frequency, mainly responsible for signal to
modulation and demodulation. RX signal into Transceiver and via Low Noise
Amplifier(LNA)
，
and mix with RX VCO signal then demodulation, amplify, via baseband
filter then output four tracks(I,IB,Q,QB) 67.708KHz Baseband signal to CPU.
The baseband signl demodulate by GMSK solution in CPU, then creation data carries on to
the deintertexture and decode etc. become 22.8 kbits/s of the data flow, then go to the
channel decode, get the numerical audio signal of 13 kbits/s, and carry on audio decoding,
restoring for the numerical signal of 64 kbits/s, then carry on a PCM decoding(D/A), it
restore analog audio signal to drive Receiver produce a sound.
The flow figure which a part of CPU, and the signal of which come from the RF or the
MIC through A/D convert or D/A convert and code or decode processing in here. One path
signal is go to the earphone, one path signal through audio PA(integrated in CPU) amplify
first then to drive speaker, and one path signal go to drive Reciver. Two path mic signals
from phone MIC and earphone MIC to CPU.
SAW filter
SAW filter
Frequency mixer
AGC amplifier and channel filter
RX signal from PA then go through transceiver to CPU
I/Q
signal